In recent years, a so-called laminate tile pole piece has been developed for an MRI. In view of such development, a plan view of the laminate tile pole piece is shown in FIG. 1A and a side view is shown in FIG. 1B. The pole piece 10 comprises a soft iron circular base plate 11, a soft iron ring 12 around the circumference of the base 11 for directing the magnetic flux into the gap between magnets, soft ferrite laminate tiles 13 and 14 and a soft iron core 15 for mounting a gradient magnetic coil. The laminate tiles 14 in the center of the base plate 11 have a greater thickness than laminate tiles 13 at the periphery of the base plate 11 to form a convex protrusion 16. The convex protrusion 16 improves the uniformity of the magnetic field.
However, the prior art laminate tile pole piece has several disadvantages. First, most laminate tiles 13, 14 have a square or rectangular shape. However, the base 11 and the ring 12 have a circular shape. Therefore, in order to fit square or rectangular tiles into a circular opening, edge filler tiles 13A are required. As shown in FIG. 1A, each edge filler tile 13A has a unique, odd shape to allow the peripheral tiles 13 to completely fill the circular base 11 and ring 12. Each edge filler tile 13A must be formed separately from other tiles 13 to create its unique shape. This increases process costs and complexity.
Second, the protrusion 16 also has a circular shape, as shown in FIG. 1A. Therefore, in order to arrange the square or rectangular central tiles 14 in a circle, edge filler tiles 14A are required, as shown in FIGS. 1A and 1B. The edge filler tiles 14A also have a unique, odd shape to allow central tiles 14 to form a circular protrusion 16. Furthermore, in order to allow central tiles 14 to fit with the peripheral tiles 13 without leaving gaps, edge filler tiles 14A also must have two different thicknesses, as shown in FIG. 1B. Each uniquely shaped edge filler tile 14A must also be formed separately from other central tiles 14. This further increases process costs.
Third, the prior art methods of forming individual laminate tiles are based on powder metallurgy or on manual metal ribbon stacking. For example, one prior art powder metallurgy laminate tile method requires pouring metal powder into individual molds and then compressing the powder to form a tile layer. Then individual pressed tile layers are glued to other tile layers to form a laminate tile. In another prior art method, thin metal sheets are slit into long strips, each strip is then covered with epoxy, the epoxy covered strips are then individually stacked into laminate bars. The laminate bars are then transferred to a compression apparatus where they are compressed and annealed. The bars are transferred to a cutting apparatus where a saw cuts the laminate bars into square laminate tiles. Alternatively, the stacked bars may be compressed and annealed prior to being impregnated with an epoxy. These batch processes require transfer of laminate materials from station to station and a high amount of manual labor because hundreds of metal layers must be stacked by hand. These processes are complicated, expensive and prone to formation of defective tiles because of human error and possible differences between each process run.